In the past, there has been proposed an organic electroluminescence element having a structure shown in FIG. 7 (see document 1 [JP 2006-331694 A]).
In this organic electroluminescence element, one electrode (cathode) 101 is placed on a surface of a substrate 104, and a light-emitting layer 103 is placed on a surface of the electrode 101 while an electron injection/transport layer 105 is interposed therebetween, and the other electrode (anode) 102 is placed on the light-emitting layer 103 while a hole injection/transport layer 106 is interposed therebetween.
Further, this organic electroluminescence element includes an encapsulating member 107 that is on the surface of the substrate 104. Therefore, in this organic electroluminescence element, light produced in the light-emitting layer 103 is emitted outside through the electrode 102 formed as a light transmissive electrode and the encapsulating member 107 made of a transparent material.
The electrode 101 with light reflectivity is made of e.g., Al, Zr, Ti, Y, Sc, Ag, or In. The electrode 102 serving as a light transmissive electrode is made of e.g. indium tin oxide (ITO) or indium zinc oxide (IZO).
To enable the organic electroluminescence element to emit light with high luminance, it is necessary to supply a large current. However, in a general organic electroluminescence element, the anode formed of an ITO film has a larger sheet resistance than that of the cathode formed of a metal film, an alloy film, a metal compound film or the like. Therefore, the anode tends to have a larger potential gradient and therefore in-plane unevenness in luminance is likely to increase.
Further, in the past, there has been proposed an organic electroluminescence lamp capable of solving the problem which would otherwise arise when a structure including an electrode formed of an ITO film prepared with sputtering is employed. Such an organic electroluminescent lamp is designed without using an electrode formed of an ITO film (see document 2 [JP 2002-502540 A]).
Document 2 discloses an electroluminescence lamp 210 as shown in FIG. 8. The electroluminescence lamp 210 includes a first electrically conductive layer 220, an electroluminescence material 230, a second electrically conductive layer 240 and a substrate 245. The first electrically conductive layer 220 is formed as a rectangular grid electrode provided with rectangular-shaped openings 250.
In this regard, document 2 describes that the first electrically conductive layer 220 and the second electrically conductive layer 240 are preferably made of conductive ink such as silver ink and carbon ink.
Furthermore, document 2 described that the first electrically conductive layer 220, the electroluminescence material 230 and the second electrically conductive layer 240 are formed with screen printing, offset printing or the like.
Note that, document 2 says that if a uniform brightness electroluminescence lamp 210 is required the density of the openings 250 must therefore be approximately constant over the lamp's surface.
In the electroluminescence lamp 210 designed as shown in FIG. 8, the first electrically conductive layer 220 includes the openings 250. Therefore, carriers are injected from the first electrically conductive layer 220 into only a region of the electroluminescence material 230 directly beneath the first electrically conductive layer 220.
Accordingly, in the electroluminescence lamp 210, it is concerned that the electroluminescent material 230 has a low luminous efficiency at regions corresponding to the openings 250 and that consequently the external quantum efficiency becomes low.